Sulfur-doped carbonaceous porous materials

ABSTRACT

The present invention relates to novel sulfur-doped carbonaceous porous materials. The present invention also relates to processes for the preparation of these materials and to the use of these materials in applications such as gas adsorption, mercury and gold capture, gas storage and as catalysts or catalyst supports.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage entry made under 35 U.S.C. § 371 ofPCT International Application No. PCT/GB2018/051977, filed Jul. 11,2018, which claims priority to Great Britain Patent Application No.1711157.6, filed Jul. 11, 2017, the entire disclosure of each of whichis incorporated herein by reference.

INTRODUCTION

The present invention relates to sulfur-doped carbonaceous porousmaterials. The present invention also relates to processes for thepreparation of these materials and to the use of these materials inapplications, such as, for example, gas adsorption, mercury and goldcapture, gas storage and as catalysts or catalyst supports.

BACKGROUND OF THE INVENTION

Microporous materials have many important applications, such as to storehydrogen to allow its use as a greener fuel, carbon dioxide capture, toprevent global warming from the production of CO₂ by burning ofconventional fuels for power, and the filtration of toxic compounds fromwaste water and gas streams to prevent environmental pollution.

To be relevant to these applications, any potential material must be notonly effective, but must also be low enough in cost to allow large scaleproduction and use. Currently, many microporous materials, such asmetal-organic frameworks or covalent organic frameworks, suffer from ahigh cost of production due to the cost of the starting materials—oftencomprising costly metals or rare organic molecules requiring complexsynthesis.

Porous carbonaceous materials have attracted great interest in recentyears due to their versatility in gas storage,¹ separations,²catalysis,³ and energy storage applications.^(4, 5) The popularity ofporous carbons is led by their relatively low cost, scalability, andease of preparation from a variety of natural and synthetic precursors.These materials possess high surface areas and pore volumes, goodthermal, chemical, and mechanical stability, high electrical and thermalconductivity, and good processability.⁶ Heteroatom doping of carbonmaterials has been suggested as the “Next Big Thing” in materialsscience and has gained a great deal of attention in the last few years.⁷

While carbonaceous materials that contain hydrogen, oxygen and nitrogenelements have been heavily studied, the use of sulfur has been exploredto a much lesser extent. The properties of porous carbons are influencedstrongly by their surface functionalities. S-doped carbonaceousmaterials have most commonly been produced by melt diffusion of sulfurinto porous carbon materials,⁸ but this approach requires an additionalsynthetic step and commonly removes all porous functionalities of thematerial. Thus, there remains a need for new methodologies into thesynthesis of s-doped carbonaceous materials, such as, for example, usinga carbonisation precursor with a high initial S-content to produce aporous, S-doped carbon directly.

Though sulfur is known to have many applications, supply still greatlyoutweighs demand, thus creating large unwanted stockpiles and a globalissue in the petrochemical industry known as the “excess sulfurproblem”.⁹

Sulfur is a waste by-product from the purification of crude oil and gasreserves, which produces ˜70 million tons of elemental sulfur annually.This quantity will likely increase as demand for energy pushes the needto use more contaminated petroleum feed-stocks. There has been interestin the use of this un-tapped, low-cost sulfur into useful materials forapplications, with the most significant advancement being a recentdevelopment known as “inverse vulcanisation”.⁹⁻¹¹ The process enablesthe production of high sulfur containing polymers by the ring-opening ofS8—a cyclic ring of 8 sulfur atoms, with the addition of a small organicmolecule crosslinker, typically a diene. This crosslinks the sulfurchains and stabilizes the product against depolymerisation.

Due to sulfur being a by-product of the petroleum industry, convertingwaste sulfur into useful polymers and related materials is an advance inwaste valorisation that is presently required.¹²

Co-polymerisation of sulfur with renewable monomers represents anadditional contribution to sustainability, as these reactions are oftensolvent free and benefit from full atom economy, further supplementingtheir Green Chemistry credentials.¹² Suggested applications for thesehigh sulfur polymers are diverse.^(9, 13) Optical applications arisefrom the high refractive index and IR transparency of the materials.¹⁴Polymeric electrodes can be produced from inverse vulcanisation to giveLi—S batteries with enhanced capacities and lifetimes.¹⁵ Sulfur polymershave also shown potential for mercury capture,¹⁶ which is enhanced ifthey are made macroporous.^(17, 18)

To date, only two reports have described microporous materialssynthesised directly from elemental sulfur. The first involved inversevulcanisation of sulfur with either diisopropenyl benzene (DIB) orlimonene, followed by carbonisation.¹⁹ The second route involved thereaction of aromatic methyl and amine-substituted monomers withelemental sulfur directly at elevated temperatures to make benzothiazolepolymers.²⁰ Both of these routes gave materials with narrow pore sizedistributions, which can be beneficial in gas separations, but also withrelatively low Brunauer-Emmett-Teller surface areas (SA_(BET)): 537 m²g⁻¹ (by nitrogen) as the highest for carbonised Sulfur-DIB co-polymer,and 751 m² g⁻¹ for the benzothiazole polymers (by argon). The organicprecursors for the S-DIB and benzothiazole polymers are, however,considerably more expensive in comparison with sulfur, making the finalS-doped polymeric high in cost, which has prevented the wide spreadproduction and use of these materials.

Therefore, there remains a need for new, cheap and easily accessiblesulfur-doped porous polymeric materials for use in applications such asadsorption, separation and gas storage.

The present invention was devised with the foregoing in mind.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided aprocess for the preparation of a sulfur-doped carbonaceous porousmaterial, the process comprising the steps of:

-   -   i) preparing a sulfur-based polymer by reacting elemental sulfur        with one or more organic crosslinking agents, wherein the        organic crosslinking agent(s) comprises two or more        carbon-carbon double bonds;    -   ii) carbonising the sulfur-based polymer of step (i) in the        presence of at least one porosity enhancement agent.

According to another aspect of the present invention, there is provideda sulfur-doped carbonaceous porous material obtainable by, obtained byor directly obtained by the process as defined herein.

According to another aspect of the present invention, there is provideda sulfur-doped carbonaceous porous material comprising:

-   -   i) greater than or equal to 5 wt % sulfur;    -   ii) a pore volume of greater than or equal to 0.75 cm³ g⁻¹; and    -   iii) a Brunauer-Emmett-Teller (BET) surface area of greater than        or equal to 1250 m² g⁻¹.

According to another aspect of the present invention, there is providedthe use of a sulfur-doped carbonaceous porous material, as definedherein, in gas adsorption.

According to another aspect of the present invention, there is providedthe use of a sulfur-doped carbonaceous porous material, as definedherein, in gas storage.

According to another aspect of the present invention, there is providedthe use of a sulfur-doped carbonaceous porous material, as definedherein, as a solid catalyst.

According to another aspect of the present invention, there is providedthe use of a sulfur-doped carbonaceous porous material, as definedherein, as a catalyst support.

According to another aspect of the present invention, there is providedthe use of a sulfur-doped carbonaceous porous material, as definedherein, in the capture of mercury.

According to another aspect of the present invention, there is providedthe use of a sulfur-doped carbonaceous porous material, as definedherein, in the capture of precious/noble metals (e.g. gold, silver,platinum, and palladium). Suitably, there is provided the use of asulfur-doped carbonaceous porous material, as defined herein, in thecapture of gold.

Features, including optional, suitable, and preferred features inrelation to one aspect of the invention may also be features, includingoptional, suitable and preferred features in relation to any otheraspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION Definitions

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean “including but notlimited to”, and they are not intended to (and do not) exclude othermoieties, additives, components, integers or steps. Throughout thedescription and claims of this specification, the singular encompassesthe plural unless the context otherwise requires. In particular, wherethe indefinite article is used, the specification is to be understood ascontemplating plurality as well as singularity, unless the contextrequires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith. All of the features disclosed in this specification(including any accompanying claims, abstract and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. The invention is notrestricted to the details of any foregoing embodiments. The inventionextends to any novel one, or any novel combination, of the featuresdisclosed in this specification (including any accompanying claims,abstract and drawings), or to any novel one, or any novel combination,of the steps of any method or process so disclosed.

The term “elemental sulfur” used herein will be understood to refer toany allotropic form of sulfur, including but not limited to, S₁₈, S₁₂,S₈, S₇ and S₆. In an embodiment, the form of elemental sulfur used isS₈.

The term “carbonaceous” used herein will be understood to refer tomaterials comprising carbon. In certain embodiments, the term“carbonaceous” refers to materials consisting essentially of carbon(i.e. comprising greater than or equal to 65 wt % carbon, suitably,greater than or equal to 75 wt % carbon).

Where the quantity or concentration of a particular component isspecified as a weight (or mass) percentage (wt % or % w/w), said weight(or mass) percentage refers to the percentage of said component byweight (or mass) relative to the total weight (or mass) of thecomposition as a whole. It will be understood by those skilled in theart that the sum of weight (or mass) percentages of all components of acomposition will total 100 wt %. However, where not all components arelisted (e.g. where compositions are said to “comprise” one or moreparticular components), the weight (or mass) percentage balance mayoptionally be made up to 100 wt % by unspecified ingredients (e.g. adiluent, such as water, or other non-essentially but suitableadditives).

Processes of the Present Invention

As described hereinbefore, the present invention provides a process forthe preparation of a sulfur-doped carbonaceous porous material, theprocess comprising the steps of:

-   -   i) preparing a sulfur-based polymer by reacting elemental sulfur        with one or more organic crosslinking agents, wherein the        organic crosslinking agent(s) comprises two or more        carbon-carbon double bonds;    -   ii) carbonising the sulfur-based polymer of step (i) in the        presence of at least one porosity enhancement agent.

The process of the present invention provides access to an array ofnovel sulfur-doped carbonaceous porous materials. Furthermore, the novelsulfur-doped carbonaceous porous materials provided by the process ofthe present invention may be utilised in numerous applications, such as,for example, gas adsorption and storage, mercury capture, gold captureand as catalyst supports.

Step (i)

It will be appreciated that any suitable reaction conditions may be usedto prepare the sulfur-based polymer of step (i) of the process definedherein.

The reaction conditions used to prepare the sulfur-based polymer of step(i) of the process will vary according to the organic crosslinkingagent(s) used. A person skilled in the art will be able to selectsuitable reaction conditions (e.g. temperature, pressures, reactiontimes, concentration etc.) to use in the preparation of the sulfur-basedpolymer of step (i) of the process.

In an embodiment, the sulfur-based polymer of step (i) is formed byreacting elemental sulfur (i.e. S₈) with one or more organiccrosslinking agents at a temperature of greater than or equal to 120° C.Suitably, the sulfur-based polymer of step (i) is formed by reactingelemental sulfur (i.e. S₈) with one or more organic crosslinking agentsat a temperature of greater than or equal to 140° C. Most suitably, thesulfur-based polymer of step (i) is formed by reacting elemental sulfur(i.e. S₈) with one or more organic crosslinking agents at a temperatureof greater than or equal to 160° C.

In another embodiment, the reaction of elemental sulfur (i.e. S₈) withone or more organic crosslinking agents to form the sulfur-based polymerof step (i) is carried out in the absence of a solvent.

In another embodiment, the reaction of elemental sulfur (i.e. S₈) withone or more organic crosslinking agents to form the sulfur-based polymerof step (i) is agitated (i.e. stirred).

In certain embodiments, an additional step of curing the reactionproduct of elemental sulfur and the one or more organic crosslinkingagents is conducted. Suitably, the reaction product of elemental sulfurand the one or more organic crosslinking agents is cured a temperatureof between 100° C. and 150° C. for between 1 hour and 36 hours. Moresuitably, the reaction product of elemental sulfur and the one or moreorganic crosslinking agents is cured a temperature of between 120° C.and 150° C. for between 6 hours and 24 hours. Most suitably, thereaction product of elemental sulfur and the one or more organiccrosslinking agents is cured a temperature of between 135° C. and 145°C. for between 6 hours and 18 hours (i.e. 12 hours).

In a further embodiment, the mass ratio of elemental sulfur to organiccrosslinking agent in step (i) of the process is between 20:80 and 95:5.Suitably, the mass ratio of elemental sulfur to organic crosslinkingagent in step (i) of the process is between 30:70 and 90:10. Moresuitably, the mass ratio of elemental sulfur to organic crosslinkingagent in step (i) of the process is between 30:70 and 80:20. Even moresuitably, the mass ratio of elemental sulfur to organic crosslinkingagent in step (i) of the process is between 30:70 and 70:30. Mostsuitably, the mass ratio of elemental sulfur to organic crosslinkingagent in step (i) of the process is between 40:60 and 60:40 (e.g.50:50).

In certain embodiments, the mass ratio of elemental sulfur to organiccrosslinking agent in step (i) of the process is between 20:80 and50:50. Suitably, the mass ratio of elemental sulfur to organiccrosslinking agent in step (i) of the process is between 20:80 and40:60. Most suitably, the mass ratio of elemental sulfur to organiccrosslinking agent in step (i) of the process is between 20:80 and30:70.

In a particular embodiment, the one or more organic crosslinking agentsof step (i) of the process comprise two double bonds (i.e. they aredienes) or three double bonds (i.e. they are trienes). Suitably, the oneor more organic crosslinking agents of step (i) of the process comprisestwo double bonds (i.e. they are dienes).

It will be appreciated that any suitable organic crosslinking agentcomprising two or more double bonds may be used to form the sulfur-basedpolymer of step (i) of the process. The person skilled in the art willappreciate that either a single organic crosslinking agent may be used,or a combination (mixture) of organic crosslinking agents may be used.Suitably, the sulfur-based polymer of step (i) is formed by reactingelemental sulfur with one organic crosslinking agent.

In an embodiment, the one or more organic crosslinking agents of thepresent invention have a molecular weight of less than 1000. Suitably,the one or more organic crosslinking agents of the present inventionhave a molecular weight of less than 500. More suitably, the one or moreorganic crosslinking agents of the present invention have a molecularweight of less than 300. Yet more suitably, the one or more organiccrosslinking agents of the present invention have a molecular weight ofless than 200. Most suitably the one or more organic crosslinking agentsof the present invention have a molecular weight of less than 150.

In an embodiment, the organic crosslinking agent is selected fromdicyclopentadiene (DCPD), di-isopropenylbenzene (DIB)tri-isopropenylbenzene (TIB), divinyl benzene (DVB), terpenes, limonene,terpinolene, myrcene, farnesene, isoprene, diallyl disulphide, tri-vinylcyclohexane, farnesol, linoleic acid, or unsaturated vegetable oils(i.e. linseed oil). Suitably, the organic crosslinking agent is selectedfrom dicyclopentadiene (DCPD), di-isopropenylbenzene (DIB)tri-isopropenylbenzene (TIB), divinyl benzene (DVB), limonene,terpinolene, myrcene, farnesene, isoprene, diallyl disulphide, tri-vinylcyclohexane, farnesol, or linoleic acid. More suitably, the organiccrosslinking agent is selected from dicyclopentadiene (DCPD),di-isopropenylbenzene (DIB) or limonene. Yet more suitably, the organiccrosslinking agent is selected from dicyclopentadiene (DCPD) ordi-isopropenylbenzene (DIB). Most suitably, the organic crosslinkingagent is dicyclopentadiene (DCPD).

In another embodiment, a blend (mixture) of organic crosslinking agentsare used. A non-limiting list of suitable blends (mixtures) of organiccrosslinking agents are given below:

-   -   dicyclopentadiene (DCPD) and limonene;    -   dicyclopentadiene (DCPD) and di-isopropenyl benzene (DIB);    -   dicyclopentadiene (DCPD), limonene and di-isopropenyl benzene        (DIB);    -   dicyclopentadiene (DCPD) and myrcene;    -   dicyclopentadiene (DCPD) and farnesene; and    -   dicyclopentadiene (DCPD) and farnesol.

It will be appreciated that the reaction between elemental sulfur andthe one or more organic crosslinking agents to form the sulfur-basedpolymer of step (i) of the process may be conducted for any suitableduration. Suitably, the reaction between elemental sulfur and the one ormore organic crosslinking agents, to form the sulfur-based polymer ofstep (i) of the process, is conducted for between 5 minutes and 12hours. More suitably, the reaction between elemental sulfur and the oneor more organic crosslinking agents, to form the sulfur-based polymer ofstep (i) of the process, is conducted for between 5 minutes and 6 hours.Yet more suitably, the reaction between elemental sulfur and the one ormore organic crosslinking agents, to form the sulfur-based polymer ofstep (i) of the process, is conducted for between 5 minutes and 3 hours.Most suitably, the reaction between elemental sulfur and the one or moreorganic crosslinking agents, to form the sulfur-based polymer of step(i) of the process, is conducted for between 5 minutes and 1 hour.

In a further embodiment, the sulfur-based polymer of step (i) of theprocess is a solid.

In yet a further embodiment, the sulfur-based polymer of step (i) of theprocess is insoluble in one or more of the following solvents: acetone,acetonitrile, chloroform, hexane, methanol, tetrahydrofuran, toluene orwater. Suitably, the sulfur-based polymer of step (i) of the process isinsoluble in all of the following solvents: acetone, acetonitrile,chloroform, hexane, methanol, tetrahydrofuran, toluene and water.

Step (ii)

It will be understood that the porosity enhancement agent of step (ii)of process may be any agent that is capable of enhancing the porosity ofthe final sulfur-doped carbonaceous porous material. Suitable porosityenhancement agents will be apparent to those skilled in the art. Anon-limiting list of suitable porosity enhancement agents includeinorganic bases (i.e. potassium hydroxide), inorganic acids (e.g.phosphoric acid), inorganic salts (i.e. NaCl), carbon dioxide (i.e.supercritical foaming) and other aerosols. Suitably, the porosityenhancement agent is selected from an inorganic base (i.e. potassiumhydroxide), an inorganic acid (e.g. phosphoric acid), or an inorganicsalt (i.e. NaCl). Most suitably, the porosity enhancement agent is aninorganic base (i.e. potassium hydroxide).

It will be appreciated that when carbon dioxide and/or an aerosol areused as the porosity enhancement agent, contact with the sulfur-basedpolymer may be conducted either prior to or during carbonisation,suitably prior to carbonisation.

In a particular embodiment, the at least one porosity enhancement agentis selected from potassium hydroxide, phosphoric acid, sodium hydroxide,sodium chloride, calcium chloride, magnesium chloride or zinc chloride.Suitably, the at least one porosity enhancement agent is selected frompotassium hydroxide, sodium hydroxide or sodium chloride.

In another embodiment, the porosity enhancement agent is an inorganicbase. Non-limiting examples of suitable inorganic bases include,potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide(LiOH), rubidium hydroxide (RbOH), caesium hydroxide (CsOH), magnesiumhydroxide (Mg(OH)₂), calcium hydroxide (Ca(OH)₂), potassium carbonate(K₂CO₃), sodium carbonate (Na₂CO₃), aluminium hydroxide (Al(OH)₃), zinchydroxide (Zn(OH)₂) or barium hydroxide (Ba(OH)₂). Suitably, theinorganic base is selected from potassium hydroxide (KOH), sodiumhydroxide (NaOH) or lithium hydroxide (LiOH). Most suitably, theinorganic base is potassium hydroxide (KOH).

In a particular embodiment, step (ii) of the process is conducted in thepresence of one porosity enhancement agent. In another embodiment, step(ii) of the process is conducted in the presence of two or more porosityenhancement agents (e.g. in the presence of two porosity enhancementagents).

It will be appreciated that the sulfur-based polymer of step (i) and theinorganic porosity enhancement agent of step (ii) may be mixed togetherprior to carbonisation. Mixing may be conducted using any suitableapparatus and for any suitable time period. It will be understood thatmixing the sulfur-based polymer of step (i) and the inorganic porosityenhancement agent of step (ii) together prior to carbonisation maximisesthe dispersion of the inorganic porosity enhancement throughout thesample of sulfur-based polymer which, following carbonisation, can aidin the generation of a broad distribution of pore sizes in the finalsulfur-doped carbonaceous porous material.

In an embodiment, the sulfur-based polymer is ground prior tocarbonisation. Suitably, the sulfur-based polymer is mechanically groundprior to carbonisation (i.e. by using a pestle and mortar, mill, orblender).

In certain embodiments, the porosity enhancement agent is selected froman inorganic base (e.g. KOH), an inorganic acid (e.g. H₃PO₄) or aninorganic salt (e.g. NaCl) and the sulfur-based polymer and the porosityenhancement agent are ground together prior to carbonisation. Suitably,the sulfur-based polymer and the porosity enhancement agent are groundtogether using a pestle and mortar, or mill, prior to carbonisation.

In other embodiments, the porosity enhancement agent is selected from aninorganic base (e.g. KOH), an inorganic acid (e.g. H₃PO₄) or aninorganic salt (e.g. NaCl) and the sulfur-based polymer and the porosityenhancement agent are ground separately, before being mixed togetherprior to carbonisation.

In another embodiment, the carbonisation of step (ii) is conducted at atemperature of between 500° C. and 1200° C. Suitably, the carbonisationof step (ii) is conducted at a temperature of between 500° C. and 1000°C. More suitably, the carbonisation of step (ii) is conducted at atemperature of between 550° C. and 950° C. Yet more suitably, thecarbonisation of step (ii) is conducted at a temperature of between 650°C. and 900° C. Even more suitably, the carbonisation of step (ii) isconducted at a temperature of between 650° C. and 850° C. Most suitably,the carbonisation of step (ii) is conducted at a temperature of between700° C. and 800° C.

In yet another embodiment, the carbonisation of step (ii) is carried outunder an inert atmosphere. It will be appreciated that any inertatmosphere may be used. Non-limiting examples of suitable inertatmospheres include nitrogen, argon, helium, neon, krypton, xenon andradon. Suitably, the inert atmosphere is a nitrogen or argon atmosphere,most suitably, nitrogen.

It will be understood that in using an inert atmosphere, the inert gasmust ideally have a purity of greater than or equal to 99%. Moresuitably, the inert gas has a purity of greater than or equal to 99.9%.Most suitably, the inert gas has a purity of greater than or equal to99.99%.

In yet another embodiment, the sulfur-based polymer of step (i) iscarbonised for a duration of between 5 minutes and 5 hours. Suitably,the sulfur-based polymer of step (i) is carbonised for a duration ofbetween 30 minutes and 5 hours. More suitably, the sulfur-based polymerof step (i) is carbonised for a duration of between 1 hour and 4 hours.Most suitably, the sulfur-based polymer of step (i) is carbonised for aduration of between 2 hours and 3 hours.

In still another embodiment, the sulfur-based polymer of step (i) iscarbonised for a duration of at least 30 minutes. Suitably, thesulfur-based polymer of step (i) is carbonised for a duration of atleast 1 hour. Most suitably, the sulfur-based polymer of step (i) iscarbonised for a duration of at least 2 hours.

In another embodiment, the mass ratio of sulfur-based polymer toporosity enhancement agent in step (ii) of the process is between 10:1and 1:10. Suitably, the mass ratio of sulfur-based polymer to porosityenhancement agent in step (ii) of the process is between 5:1 and 1:5.More suitably, the mass ratio of sulfur-based polymer to porosityenhancement agent in step (ii) of the process is between 3:1 and 1:3.Yet more suitably, the mass ratio of sulfur-based polymer to porosityenhancement agent in step (ii) of the process is between 2:1 and 1:2.Even more suitably, the mass ratio of sulfur-based polymer to porosityenhancement agent in step (ii) of the process is between 2:1 and 1:1.Most suitably, the mass ratio of sulfur-based polymer to porosityenhancement agent in step (ii) of the process is 1:1.

Sulfur-Doped Carbonaceous Porous Materials of the Present Invention

In another aspect, the present invention provides a sulfur-dopedcarbonaceous porous material obtainable by, obtained by or directlyobtained by any process of the present invention defined herein.

The process of the present invention advantageously provides novelsulfur-doped carbonaceous porous materials with a high surface areaand/or high pore volume.

In an embodiment, the sulfur-doped carbonaceous porous materials of thepresent invention have a Brunauer-Emmett-Teller (BET) surface area ofgreater than or equal to 1000 m² g⁻¹. Suitably, the sulfur-dopedcarbonaceous porous materials of the present invention have a BETsurface area of greater than or equal to 1250 m² g⁻¹, more suitably,greater than or equal to 500 m² g⁻¹, yet more suitably greater than orequal to 1500 m² g⁻¹, and even more suitably greater than or equal to1750 m² g⁻¹, and most suitably, greater than or equal to 2000 m² g⁻¹.

In another embodiment, the sulfur-doped carbonaceous porous materials ofthe present invention have a pore volume of greater than or equal to0.75 cm³ g⁻¹. Suitably, the sulfur-doped carbonaceous porous materialsof the present invention have a pore volume of greater than or equal to0.85 cm³ g⁻¹, more suitably, greater than or equal to 0.9 cm³ g⁻¹ andmost suitably greater than or equal to 0.95 cm³ g⁻¹.

In yet another embodiment, the sulfur-doped carbonaceous porous materialcomprises greater than or equal to 5 wt % sulfur. Suitably, thesulfur-doped carbonaceous material comprises greater than or equal to 8wt % sulfur, more suitably, greater than or equal to 10 wt % sulfur, andmost suitably, greater than or equal to 12 wt % sulfur.

In still another embodiment, the sulfur-doped carbonaceous porousmaterial comprises between 5 wt % and 50 wt % sulfur. Suitably, thesulfur-doped carbonaceous porous material comprises between 5 wt % and30 wt % sulfur. More suitably, the sulfur-doped carbonaceous porousmaterial comprises between 5 wt % and 25 wt % sulfur. Yet more suitably,the sulfur-doped carbonaceous porous material comprises between 5 wt %and 20 wt % sulfur. Most suitably, the sulfur-doped carbonaceous porousmaterial comprises between 10 wt % and 15 wt % sulfur.

In a further embodiment, the sulfur-doped carbonaceous porous materialcomprises between 65 wt % and 95 wt % carbon. Suitably, the sulfur-dopedcarbonaceous porous material comprises between 70 wt % and 90 wt %carbon, more suitably, between 70 wt % and 85 wt % carbon, and mostsuitably, between 75 wt % and 85 wt % carbon.

In an embodiment, the sulfur-doped carbonaceous porous materialcomprises greater than or equal to 90 wt % carbon, hydrogen and sulfur.Suitably, the sulfur-doped carbonaceous porous material comprisesgreater than or equal to 95 wt % carbon, hydrogen and sulfur. Moresuitably, the sulfur-doped carbonaceous porous material comprisesgreater than or equal to 99 wt % carbon, hydrogen and sulfur. Mostsuitably, the sulfur-doped carbonaceous porous material comprisesgreater than or equal to 99.5 wt % carbon, hydrogen and sulfur.

In another embodiment, the sulfur-doped carbonaceous porous materialconsists essentially of carbon, hydrogen and sulfur. Suitably, thesulfur-doped carbonaceous porous material consists of carbon, hydrogenand sulfur. More suitably, the sulfur-doped carbonaceous porous materialconsists entirely of carbon, hydrogen and sulfur.

In certain embodiments, the sulfur-doped carbonaceous porous material ischaracterised in that the Powder X-Ray Diffraction (PXRD) pattern has a(broad) diffraction peak at a 2θ value of 25°, with an error range in 2θvalue of ±2°.

In other embodiments, the sulfur-doped carbonaceous porous material ischaracterised in that the Powder X-Ray Diffraction (PXRD) pattern has a(broad) diffraction peak at a 2θ value of 43°, with an error range in 2θvalue of ±2°.

Particular sulfur-doped carbonaceous porous materials include any of thematerials exemplified in the present application, and, in particular,any material characterised in that the Powder X-Ray Diffraction (PXRD)pattern thereof is as shown in any one of traces 4K-S-DCPD-750 or1K-S-DCPD-750 in FIG. 10 .

In another aspect of the present invention, there is provided asulfur-doped carbonaceous porous material comprising:

-   -   i) greater than or equal to 5 wt % sulfur;    -   ii) a pore volume of greater than or equal to 0.75 cm³ g⁻¹; and    -   iii) a Brunauer-Emmett-Teller (BET) surface area of greater than        or equal to 1250 m² g⁻¹.

In an embodiment, the sulfur-doped carbonaceous porous materialcomprises micropores and mesopores.

In another embodiment, the sulfur-doped carbonaceous porous material hasa micropore volume of greater than or equal to 0.25 cm³ g⁻¹. Suitably,the sulfur-doped carbonaceous porous material has a micropore volume ofgreater than or equal to 0.35 cm³ g⁻¹. Most suitably, the sulfur-dopedcarbonaceous porous material has a micropore volume of greater than orequal to 0.45 cm³ g⁻¹.

In a further embodiment, the sulfur-doped carbonaceous porous materialis a solid.

It will be understood that features, including optional, suitable, andpreferred features in relation to any one of the aspects of the presentinvention detailed above may also be features, including optional,suitable and preferred features in relation to any other aspects of theinvention (i.e. the product per se).

Particular Embodiments

In an embodiment, the process of the present invention comprises thesteps of:

-   -   i) preparing a sulfur-based polymer by reacting elemental sulfur        with one or more organic crosslinking agents, wherein the        organic crosslinking agent(s) comprises two or more        carbon-carbon double bonds;    -   ii) carbonising the sulfur-based polymer of step (i) in the        presence of an inorganic base (e.g. KOH), an inorganic acid        (e.g. H₃PO₄) or an inorganic salt (e.g. NaCl);        -   wherein the mass ratio of sulfur-based polymer to inorganic            base, inorganic acid or inorganic salt is between 5:1 and            1:5.

In another embodiment, the process of the present invention comprisesthe steps of:

-   -   i) preparing a sulfur-based polymer by reacting elemental sulfur        with one or more organic crosslinking agents, wherein the        organic crosslinking agent(s) comprises two or more        carbon-carbon double bonds;    -   ii) carbonising the sulfur-based polymer of step (i) in the        presence of an inorganic base (e.g. KOH);        -   wherein the mass ratio of sulfur-based polymer to inorganic            base is between 5:1 and 1:5 and the carbonisation of            step (ii) is conducted at a temperature of between 650° C.            and 850° C.

In another embodiment, the process of the present invention comprisesthe steps of:

-   -   i) preparing a sulfur-based polymer by reacting elemental sulfur        with one or more organic crosslinking agents, wherein the        organic crosslinking agent(s) comprises two carbon-carbon double        bonds;    -   ii) carbonising the sulfur-based polymer of step (i) in the        presence of an inorganic base (e.g. KOH) for at least 2 hours;        -   wherein the mass ratio of sulfur-based polymer to inorganic            base is between 3:1 and 1:3 and the carbonisation of            step (ii) is conducted at a temperature of between 650° C.            and 850° C.

In another embodiment, the process of the present invention comprisesthe steps of:

-   -   i) preparing a sulfur-based polymer by reacting elemental sulfur        with one or more organic crosslinking agents, wherein the        organic crosslinking agent(s) comprises two carbon-carbon double        bonds;    -   ii) carbonising the sulfur-based polymer of step (i) in the        presence of an inorganic base (e.g. KOH) for between 1 hour and        4 hours;        -   wherein the mass ratio of sulfur-based polymer to inorganic            base is between 3:1 and 1:3 and the carbonisation of            step (ii) is conducted at a temperature of between 650° C.            and 850° C.

In another embodiment, the process of the present invention comprisesthe steps of:

-   -   i) preparing a sulfur-based polymer by reacting elemental sulfur        with an organic crosslinking agent (e.g. dicyclopentadiene),        wherein the organic crosslinking agent comprises two        carbon-carbon double bonds and has a molecular weight of less        than 300;    -   ii) carbonising the sulfur-based polymer of step (i) in the        presence of an inorganic base (e.g. KOH) for at least 2 hours;        -   wherein the mass ratio of sulfur-based polymer to inorganic            base is between 3:1 and 1:3 and the carbonisation of            step (ii) is conducted at a temperature of between 650° C.            and 850° C.

In another embodiment, the process of the present invention comprisesthe steps of:

-   -   i) preparing a sulfur-based polymer by reacting elemental sulfur        with an organic crosslinking agent (e.g. dicyclopentadiene) at a        temperature of greater than or equal to 140° C., wherein the        organic crosslinking agent comprises two carbon-carbon double        bonds and has a molecular weight of less than 200;    -   ii) carbonising the sulfur-based polymer of step (i) in the        presence of an inorganic base (e.g. KOH) for at least 2 hours;        -   wherein the mass ratio of sulfur-based polymer to inorganic            base is between 3:1 and 1:3 and the carbonisation of            step (ii) is conducted at a temperature of between 650° C.            and 850° C.

In another embodiment, the process of the present invention comprisesthe steps of:

-   -   i) preparing a sulfur-based polymer by reacting elemental sulfur        with dicyclopentadiene (DCPD) at a temperature of greater than        or equal to 140° C.;    -   ii) carbonising the sulfur-based polymer of step (i) in the        presence of an inorganic base (e.g. KOH) for at least 2 hours;        -   wherein the mass ratio of sulfur-based polymer to inorganic            base is 1:1 and the carbonisation of step (ii) is conducted            at a temperature of between 700° C. and 800° C.            Applications

The process of the present invention provides access to the novelsulfur-doped carbonaceous porous materials that may be utilised innumerous applications, such as, for example, gas adsorption, separationand storage, mercury capture, gold capture and as catalysts (i.e. foroxygen reduction reactions) or catalytic supports.

Thus, in one aspect, there is provided the use of a sulfur-dopedcarbonaceous porous material, as defined herein, in gas adsorption.

In another aspect of the present invention, there is provided the use ofa sulfur-doped carbonaceous porous material, as defined herein, in gasseparation.

In yet another aspect of the present invention, there is provided theuse of a sulfur-doped carbonaceous porous material, as defined herein,in gas storage.

As the materials of the present invention are porous, they areparticularly well suited to storing and absorbing gas. It will beappreciated that the sulfur-doped carbonaceous porous materials of thepresent invention may therefore be used to store, absorb and/or separateany suitable gas. Furthermore, it will be understood that the gasstorage/absorption capabilities of the sulfur-doped carbonaceous porousmaterials of the present invention, will vary according to the specificamount and nature of organic crosslinking agent used in step (i) of thepresent process.

Suitably, the gas to be stored, absorbed and/or separated is selectedfrom methane, hydrogen or carbon dioxide. Most suitably, the gas to bestored, absorbed and/or separated is carbon dioxide.

In a further aspect of the present invention, there is provided the useof a sulfur-doped carbonaceous porous material, as defined herein, as acatalyst support. In an embodiment, there is provided the use of asulfur-doped carbonaceous porous material, as defined herein, as a solidcatalyst support.

As the materials of the present invention have an exceptionally highsurface area, they are particularly well suited to acting as a supportsfor various catalysts. It will be appreciated that the sulfur-dopedcarbonaceous porous material of the present invention may be used as asupport for any suitable catalyst. Suitably, the sulfur-dopedcarbonaceous porous material of the present invention may be used as asolid support for catalysts comprising precious/noble metals (i.e.palladium, platinum, gold and/or silver). More suitably, thesulfur-doped carbonaceous porous material of the present invention maybe used as a solid support for catalytic and electro-catalyticprocesses.

Sulfur atoms are known to have an excellent affinity for certainelements such as, for example, toxic metals such as mercury or cadmiumand precious/noble metals such as gold, silver, platinum, and palladium.Thus, given that the materials of the present invention have a highdoping of sulfur atoms they are particularly well suited for use inextracting (capturing) mercury and/or precious/noble metals (e.g. gold,silver, platinum, and palladium) from various feedstocks. Suitablefeedstocks from which mercury and/or precious/noble metal (gold, silver,platinum, and palladium) may be extracted include solutions and/ordispersions of mercury and/or the precious/noble metal.

Thus, in another aspect of the present invention, there is provided theuse of a sulfur-doped carbonaceous porous material, as defined herein,in the capture of mercury.

In yet a further aspect of the present invention, there is provided theuse of a sulfur-doped carbonaceous porous material, as defined herein,in the capture of precious/noble metals (e.g. gold, silver, platinum,and palladium).

In an embodiment, there is provided the use of a sulfur-dopedcarbonaceous porous material, as defined herein, in the capture of gold,platinum and/or palladium. Suitably, there is provided the use of asulfur-doped carbonaceous porous material, as defined herein, in thecapture of gold.

EXAMPLES Description of Drawings

Embodiments of the invention will be described, by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 shows the synthesis of the hypercrosslinked polymers and thesubsequent carbonization method.

FIG. 2 shows the nitrogen adsorption-desorption isotherms of KOHactivated S-DCPD carbons at 77.3 K (the adsorption and desorptionbranches are labelled with filled and empty symbols, respectively).

FIG. 3 shows the FE-SEM images of a) S-DCPD-850 and c) 1K-S-DCPD-750.TEM images of b) S-DCPD-850 and d) 1K-S-DCPD-750. Higher e) FE-SEM andf) TEM magnification of 1K-S-DCPD-750.

FIG. 4 shows a) CO₂ sorption isotherms at 298 K over pressure range 0-1bar. b) CH₄ sorption isotherms at 298 K over pressure range 0-1 bar. c)H2 sorption isotherms at 77 K over pressure range 0-1 bar. d) CO₂ andCH₄ sorption isotherms at 298 K and H2 sorption isotherms at 77 K of1K-S-DCPD-750 over pressure range 0 10 bar.

FIG. 5 shows the adsorption isotherm of mercury (as aqueous HgCl₂) intosamples of carbonized sulfur polymer (orange circles) and conventionalactivated carbon (black squares), with Langmuir isotherm fitting shownas dashed red and black lines.

FIG. 6 shows photographs of a) directly carbonized S-DCPD resulting in alarge grey metallic monolith and b) KOH activated S-DCPD carbon blackpowder.

FIG. 7 shows the nitrogen adsorption-desorption isotherms of directlycarbonized S-DCPD at 77.3 K (the adsorption and desorption branches arelabelled with filled and empty symbols, respectively).

FIG. 8 shows the pore size distributions of carbonised S-DCPD calculatedby non-local density functional theory (NL-DFT).

FIG. 9 shows the HR-TEM images of a) S-DCPD-850 and b) 1K-S-DCPD-750with higher resolution images of 1K S-DCPD-750 at c) 20 nm and d) 10 nmscale.

FIG. 10 shows the PXRD patterns of carbonized S-DCPD samples. Samples1K-S-DCPD-750 and 4K-S-DCPD-750 contain additional alumina peaksassociated from the ceramic boat and/or use of pestle and mortar.

FIG. 11 shows the CO₂ and CH₄ sorption isotherms at 298 K and H2sorption isotherms at 77 K of S-DCPD-850 over a pressure range of 0-10bar.

FIG. 12 shows the uptake of various metal ions from deionised waterusing 1K-S-DCPD-750 and activated charcoal.

FIG. 13 shows the capture of gold from deionised water using1K-S-DCPD-750 and activated charcoal.

SULFUR-DOPED CARBONACEOUS POROUS MATERIAL NOMENCLATURE

In the illustrative examples hereinbelow, the following nomenclature isused to denote each of the sulfur-doped carbonaceous porous materialsprepared:nB-S-[Crosslinker]-Δwherein:

-   -   n is the mass ratio of porosity enhancement agent (e.g.        inorganic base) to sulfur-based polymer;    -   B is the porosity enhancement agent (e.g. potassium hydroxide);    -   S is sulfur;    -   [Crosslinker] is the crosslinker used (e.g.        [DCPD]=dicyclopentadiene)    -   Δ is the temperature at which carbonisation is conducted.

For example, using the above labelling system, the carbonisation of asulfur-based polymer (formed from the reaction between elemental sulfurand dicyclopentadiene) with a 1:1 mass ratio of KOH at 750° C. would begiven the following label—1K-S-DCPD-750.

Materials

Dicyclopentadiene (DCPD) was purchased from Tokyo Chemicals Industry.Sulfur and potassium hydroxide were purchased from Sigma Aldrich. Highpurity nitrogen was purchased from BOC. All chemicals were used asreceived without any further purification. Distilled water was used inpurifications.

Synthesis of S-DCPD

Polymerisations were carried out in open glass samples vials (12 or 40mL volume) in aluminium heating blocks, with heating and stirringprovided by electronic hotplates and magnetic stirrer bars. Allreactions were begun by allowing the sulfur to fully melt, at 160° C.,before adding the organic crosslinking agent directly. Sulfur:organiccrosslinking agent mass ratios were varied, but total mass was typicallybetween 5 and 20 g.

Using DCPD as the crosslinker, heating was maintained at 160° C. for 2hours (the reaction vitrifies after typically ˜20 minutes). The colourbecame increasingly dark during the polymerisation, resulting in a blacksolid product. Moulded objects were prepared by polymerising thecrosslinker (DCPD) and sulfur together as normal in a stirred glassvial, to ensure homogeneous mixing, before transferring them into asilicone mould and curing in an oven at 140° C. for 12 hours. The pointto transfer the reaction mixture from the stirred vial to the mould wastaken as the point at which an aliquot of the reaction mixture, whenremoved on a spatula and allowed to cool to room temperature, would nolonger visibly separate to clear organic monomer, and precipitatedyellow sulfur powder, but instead remain as a homogeneous brown viscousliquid.

Synthesis of Directly Carbonised Materials (Comparative Examples)

In a typical procedure, S-DCPD (300 mg) was homogeneously ground using apestle and mortar. The polymer was placed in a ceramic boat and insertedwithin a tube furnace. The furnace was purged with N₂ at roomtemperature for 30 min, heated to the specified temperature at a rate of5° C. min⁻¹, held at the set temperature for the associated time, andfinally cooled to room temperature. The material was used withoutfurther purification.

Synthesis of KOH Activated Carbonised Materials

In a typical procedure, S-DCPD (1.0 g) and the associated amount of KOHwas homogeneously ground using a pestle and mortar. The mixture wasplaced in a ceramic boat and inserted within a tube furnace. The furnacewas purged with N₂ at room temperature for 30 min, heated to thespecified temperature at a rate of 5° C. min⁻¹, held at the settemperature for 2 h, and finally cooled to room temperature. The residuewas washed thoroughly with DI water and 1 M HCl until the filtrateattained pH 7. The resultant carbons were dried under vacuum for 1 d at70° C.

Mercury Uptake Studies

A stock solution of mercury was made by dissolving HgCl₂ (338 mg) indeionised water (250 mL) to produce a concentration of 1000 ppm, thiswas then used to prepare the test solutions of 20, 100, 500 and 750 ppmby serial dilutions. Activated charcoal (Sigma Aldrich, measured at 594m² g⁻¹) and 1K-S-DCPD were coarsely ground and screened through a 45mesh sieve to ensure particles no larger than 350 microns. 12 mL of eachsolution was decanted in to a series of glass vials along with either15, 30 or 60 mg of 1K-S-DCPD or activated charcoal, the vials were thencapped and placed on a roller for 1 hour at room temperature. After 1hour, the vials were removed and the test solutions filtered into cleansample vials using a 0.22 μm filter and a polypropylene syringe. Sampleswere analysed by ICP-OES, conducted using an Agilent 5110. The data werefitted to a Langmuir isotherm, q_(A)=(K.C_(e).Q_(sat))/(1+K.C_(e)),where qA=mg adsorbate per g adsorbent (mg g⁻¹), K=adsorption parameter(L mg⁻¹), Ce=equilibrium concentration (mg L⁻¹) and Q_(sat)=maximumcapacity (mg g⁻¹)

Gas Sorption

The porous properties of the networks were investigated by nitrogenadsorption and desorption at 77.3 K using an ASAP2420 volumetricadsorption analyser (Micrometrics Instrument Corporation). 1 bar CO₂ andCH₄ isotherms at 298 K and H₂ isotherms at 77.3 K were collected on aMicromeritics ASAP2020 and ASAP2050. 10 bar CO₂ and CH₄ isotherms at 298K and H₂ isotherms at 77.3 K were collected using a MicromeriticsASAP2050. All samples were degassed at 100° C. for 15 h under vacuum(10⁻⁵ bar) before analysis.

Pore Structure Analysis

Pore structure properties of the samples were determined via nitrogenadsorption and desorption at 77.3 K using a volumetric technique on anASAP2420 adsorption analyser (Micromeritics Instrument Corporation).Before analysis, the samples were degassed at 100° C. for 15 h undervacuum (10⁻⁵ bar).

Brunauer-Emmett-Teller (BET) surface area was obtained in the relativepressure (P/P₀) range of 0.05-0.20, and total pore volume (V_(t)) wasdetermined from the amount of nitrogen adsorbed at P/P₀=ca. 0.99.

FE-SEM

High resolution imaging of the polymer morphology was achieved using aHitachi S-4800 cold field emission scanning electron microscope(FE-SEM).

HR-TEM

High-resolution transmission electron microscopy (HR-TEM) was performedusing a JEOL 2100FCS microscope, equipped with a Schottky field emissiongun, operating at 200 kV. Bright field images were recorded inconventional TEM illumination mode. Chemical analyses were performed byenergy dispersive x-ray spectroscopy using a windowless EDAXspectrometer.

TEM specimens were produced by ultrasonically dispersing powder inanalytical grade methanol, the suspension was then dropped onto coppermesh grids with holey carbon support films and allowed to dry.

Elemental Analysis

CHN elemental analysis was conducted on a Thermo FlashEA 1112.

PXRD

Powder X-ray diffraction (PXRD) data were collected in transmission modeon loose powder samples held on thin Mylar film in Stainless steel wellplates on a Panalytical X'Pert PRO MPD equipped with an high throughputscreening (HTS) XYZ stage, X-ray focusing mirror, ½ degree divergenceslit, 0.04 degree soller slits, 4 mm beam mask and PIXcel detector,using Cu Kα radiation. Data were measured over the range 5-50° 2θ in0.013° steps over 60 minutes.

Design and Porosity of S-Doped Carbons

S-DCPD was initially carbonised under a flow of nitrogen at 750° C. for1 h as a direct comparison with the previously reported carbonisedinverse vulcansed polymer,¹⁹ and the product was denoted asS-DCPD-750-1. This material became microporous with a SA_(BET) of 403 m²g⁻¹. A yellow powder appeared in the tube furnace exhaust due to theleeching of elemental sulfur, and the resultant material was a shinygrey/black monolith (FIG. 6 ).

With the aim of increasing the surface areas, S-DCPD was furthercarbonised for an extended time of 2 h and another sample was carbonisedat a higher temperature, 850° C., for 2 h (S-DCPD-750-2 and S-DCPD-850,respectively). The nitrogen sorption isotherms for S-DCPD-750-1 andS-DCPD-750-2 were very similar (FIG. 7 ); both exhibited Type Iabehaviour where most of the nitrogen uptake occurs at P/P₀<0.02,indicating narrow micropores (FIG. 8 ), resulting in a SA_(BET) of 415m² g⁻¹ for S-DCPD-750-2.

S-DCPD-850 also showed a Type Ia isotherm, but the somewhat larger gasuptake at the microporous region resulted in a higher SA_(BET) of 511 m²g⁻¹. These surface areas are comparable to previously reportedcarbonised inverse vulcansed polymers.¹⁹

We next moved to a different carbonisation approach with the aid of KOHas a chemical activating agent to target higher surface area S-dopedcarbons. S-DCPD was synthesised and thoroughly mixed with varyingamounts of KOH before being carbonised under a nitrogen flow for 2 h(FIG. 1 ). The carbons are referred to as nK-S-DCPD-Δ where n is themass ratio of KOH to S-DCPD and Δ signifies the carbonisationtemperature. The nitrogen sorption isotherms of the KOH-activatedcarbonised S-DCPD showed high levels of microporosity in all samples(FIG. 2 ). The physical properties of these carbons and their precursorsare summarized in Table 1.

0.5K-S-DCPD-750 showed a Type Ib isotherm indicating high levels ofmicroporosity with pore size distributions over a broader range comparedwith the directly carbonised samples (FIG. 8 ). As the KOH to S-DCPDratio was increased to 1:1 in 1K-S-DCPD-750, the nitrogen sorptionincreases, especially in the P/P₀<0.02 microporous region, resulting ina higher micropore volume (0.80 versus 0.51 cm³ g⁻¹) and an increase inSA_(BET) (2216 m² g⁻¹ versus 1792 m² g⁻¹). Further increases in the KOHquantity in 2K-S-DCPD-750 and 4K-S-DCPD-750 resulted in some Type IVacharacter, where a hysteresis loop gradually appeared at P/P₀=0.5indicative of the development of mesopores. The SA_(BET) values forthese hierarchically-porous materials were 2197 and 1520 m² g⁻¹,respectively. The micropore percentage fell from 73% in 1K-S-DCPD-750 to56% in 2K-S-DCPD-750 and 28% in 4K-S-DCPD-750, perhaps because of anoversaturation of the KOH activating agent causing micropore collapse.Since S-DCPD contains 50 wt % sulfur, smaller quantities of KOHactivating agent are required compared with conventional carbonisations,where the precursor contains a much higher carbon content.²³

Higher carbonisation temperatures (850° C.) were also tested with1K-S-DCPD-850 since it is known that higher surface areas can beachieved with temperature optimisation,¹ but the resulting carbonyielded a Type Ib isotherm with a SA_(BET) of 1599 m² g⁻¹. Thecarbonised S-DCPD materials retain a significant amount of their parentsulfur heteroatom in their structure—up to 18.16 wt %—showing thatincorporation of sulfur into the porous carbon is possible when usinginverse vulcansed polymers as a carbonisation precursor (Table 2). TheSA_(BET) of 2216 m² g⁻¹ for 1K-S-DCPD-750 outperforms other microporousS-doped carbons,²⁴ including carbonisation precursors that wereinherently porous and more costly.²⁵

TABLE 1 Physical properties, H₂, CO₂, and CH₄ uptake of KOH activatedS-DCPD carbons. Surface area Pore volume^(a) (m² g⁻¹) (cm³ g⁻¹) Gasuptake BET Langmuir Micro- Total CO₂ ^(c) CH₄ ^(d) H₂ ^(e) Sample methodmethod pore pore^(b) (mmol g⁻¹) (mmol g⁻¹) (wt %) 0.5KS-DCPD-750 17922379 0.51 1.00 2.01 1.07 1.99 1KS-DCPD-750 2216 2976 0.80 1.09 2.20 1.032.09 2KS-DCPD-750 2197 3015 0.68 1.21 1.79 0.58 1.88 4KS-DCPD-750 15201995 0.26 0.92 1.29 0.50 1.40 1KS-DCPD-850 1599 2226 0.48 0.84 1.31 0.571.41 ^(a)Calculated by single point pore volume. ^(b)Total pore volumeat P/P₀ = 0.99. ^(c)CO₂ uptake at 298K and 1 bar. ^(d)CH₄ uptake at 298Kand 1 bar. ^(e)H₂ uptake at 77K and 1 bar.

TABLE 2 Carbonisation yields and CHNS elemental analysis of S-dopedporous carbon products. Sample Yield (%) C H S S-DCPD-750-1 36 75.850.66 18.16 S-DCPD-750-2 35 77.25 0.63 17.67 S-DCPD-850 32 81.86 0.5011.89 0.5K-S-DCPD-750 23 74.91 0.35 13.54 1K-S-DCPD-750 34 74.14 0.5513.27 2K-S-DCPD-750 14 78.37 0.95 12.77 4K-S-DCPD-750 16 77.98 0.5512.73 1K-S-DCPD-850 34 69.40 0.87 9.55Characterisation of Carbons

Field emission scanning electron microscopy (FE-SEM) and transmissionelectron microscopy (TEM) was used to study the morphology of carbonisedS-DCPD products (FIG. 3 ). The shiny, monolithic structure from directlycarbonising S-DCPD in S-DCPD-850 is shown in FIG. 3 a . The observedstructure was smooth with few signs of pores on the surface. TEM of thesample also backed up this observation since the white spots that aretypically indicative of pores were not apparent (FIG. 3 b ).

The KOH-activated carbonised product, 1K-S-DCPD-750, was a black powder(FIG. 6 b ) and its rough, particulate surface was apparent under FE-SEM(FIG. 3 c & e). TEM of the porous carbon indicated high porosity, and alower density was structure observed (FIG. 3 d & f).

High-resolution transmission electron microscopy (HR-TEM) was also usedto examine both types of products and was found that the KOH-activatedsample resulted in a more fibrous network due to its greater porosity(FIG. 9 ).

The morphology of the KOH-activated sample was also observed to be morehomogeneous when scanning across the material compared to the directlycarbonised sample, which can be advantageous.

Powder X-ray diffraction patterns of the carbonised products showed twobroad characteristic peaks located at 25 and 43° (FIG. 10 ),corresponding to the (002) and (100) planes of hexagonal graphite,respectively, revealing the presence of an amorphous structure and a lowdegree of graphitisation.²⁶

CO₂, CH₄ and H₂ Storage

The affinities of the S-DCPD carbons towards small gas sorption (CO₂,CH₄, and H₂) were studied (FIG. 4 ).

The CO₂ uptakes for the KOH-activated materials were tested at roomtemperature (ca. 298 K) with the full isotherms shown in FIG. 4 a .Table 1 summarizes the amount of CO₂ absorbed by each material at apressure of 1 bar. The CO₂ uptake was roughly proportional to thesurface area of each material, with a CO₂ uptake of up to 2.20 mmol g⁻¹for 1K-S-DCPD-750, outperforming recent reports of sulfur-containingmicroporous polymers,²⁰ previous carbonised inverse-vulcansedpolymers,¹⁹ sulfur-containing hypercrosslinked microporous polymers,²⁷and microporous networks COF-6,²⁸ CMP-1,²⁹ and highly porous PAF-1.³⁰

The CH₄ sorption behaviour was also tested at 298 K and 1 bar with anuptake of up to 1.07 mmol g⁻¹ for 0.5KS-DCPD-750 (FIG. 4 b ).

H₂ uptakes tested at 77 K and 1 bar were high with all KOH-activatedsamples, with an uptake of 2.09 wt % observed from 1K-S-DCPD-750 (FIG. 4c ). The large uptakes are due to H₂ being purely attracted to a largesurface via physisorption as a result of weak van der Waalsinteractions.

The H₂ uptake is more than three times larger than the previouslyreported carbonised inverse vulcansed polymers; this a dramaticimprovement for this cheap synthetic method,¹⁹ although more strikingresults were found at higher gas pressures, as discussed below.

The absorption of small gases were also evaluated at pressures of up to10 bar for the optimised sample, 1K-S-DCPD-750 (FIG. 4 d ). Thismaterial adsorbed up to 10.1 mmol g⁻¹ of CO₂ at 298 K with no sign ofsaturation, matching and outperforming more costly materials such ascarbonised polyacrylonitrile AC-3000,³¹ mesoporous silica templatedcarbon IBN-9,³² and directly carbonised MOF-74 and MIL-53.³³

1K-S-DCPD-750 adsorbs 2.74 wt % H2 at 77 K and 10 bar, outperformingindustrial BPL activated carbon,²⁸ and exceeding porous carbons12ACA-800 made from carbon aerogel via subcritical drying,³⁴ AC-C4(activated at very high temperatures with further activation using CO₂gas),³⁵ and even porous carbons measured at high pressures of over 60bar.³⁶

Mercury Capture Studies

The sulfur-doping in the structure of these microporous carbons may havefurther benefits, such as providing anchor sites for metal catalysts.The combination of high surfaces areas, hierarchical porosity, and highsulfur loading is also very attractive for the removal of trace heavymetals from water. Mercury pollution from industrial wastewater is asignificant global health concern because of its relatively highsolubility in water and tendency to bioaccumulate and cause severe toxiceffects.³⁷

Sulfur is known to have a high affinity for mercury, and therefore1K-S-DCPD-750 was tested for the capture of HgCl₂ from water (FIG. 5 ).1K-S-DCPD-750 showed a greatly enhanced uptake of mercury in comparisonto activated carbon, especially at low mercury concentrations. Activatedcarbons are frequently used for the adsorption of mercury fromwastewater, and they generally show maximum Hg uptakes in the ˜10-500 mgg⁻¹ range.³⁸

At an equilibrium Hg concentration of ˜10 ppm, 1K-S-DCPD-750 absorbedover 15 times more Hg than the activated carbon control (151 mg g⁻¹versus 7.8 mg g⁻¹). Fitting these data to a Langmuir isotherm alsoindicated a higher saturation capacity for the sulfur loaded material(850 mg g⁻¹ vs. 498 mg g⁻¹) and adsorption parameters that were over 20times higher (0.058 L mg⁻¹ vs. 0.0028 L mg⁻¹). Absorption of mercury atlow concentrations (<1 mg g⁻¹) has particular practical relevance. Forexample, the Environmental Protection Agency has set a maximumcontaminant level goal for mercury of 0.002 mg/L, or 1×10⁻⁶ mg/g.³⁹

Capture of Other Metals

100 ppm solutions (50 ml) of chromium, cobalt, copper, manganese, iron,nickel and mercury were made up from stock solutions respective metalsalts (either chloride or nitrate forms) and de-ionised water. Activatedcharcoal and 1K-S-DCPD-750 were coarsely ground and screened through a45 Mesh sieve to ensure that all tests would contain particles no largerthan 350 microns. 15 ml plastic vials were loaded with 30 mg of either1K-S-DCPD-750 or activated charcoal and 12 ml of the chosen metalsolution, the tubes were then capped and placed on a roller for 1 hourat room temperature. Multiple metals were tested at a time by conductingtests in parallel. After 1 hour, the vials were removed and stood in arack to allow the particulates to settle, whilst a 1 ml aliquot wasremoved for analysis. The samples were diluted by a factor of 10 byadding the 1 ml aliquots each to a vial containing 9 ml of de-ionisedwater. Samples were analysed along with a water blank and 100 ppmcontrol samples of each metal using the same calibration method on theICP-OES, with the data being corrected post collection. ICP-OES analysiswas conducted using an Agilent 5110.

Results from the application of the above described method are depictedin FIG. 12 .

Capture of Gold

A 1,000 ppm gold solution (250 ml) was made up from a stock solution ofChloroauric acid (HAuCl₄) and deionised water, with the pH adjusted to3-4 with the addition of Hydrochloric acid. Activated charcoal and1K-S-DCPD-750 were coarsely ground and screened through a 45 Mesh sieveto ensure that all tests would contain particles no larger than 350microns. 15 ml plastic vials were loaded with 5, 10, 20, 40 and 80 mg ofeither 1K-S-DCPD-750 or activated charcoal and 12 ml of the goldsolution, the tubes were then capped and placed on a roller for 1 hourat room temperature. After 1 hour, the vials were removed and stood in arack to allow the particulates to settle, whilst a 1 ml aliquot wasremoved for analysis. The samples were diluted by a factor of 10 byadding the 1 ml aliquots each to a vial containing 9 ml of de-ionisedwater. Samples were analysed along with a water blank and a 1,000 ppmcontrol sample using the same calibration method on the ICP-OES, withthe data being corrected post collection. ICP-OES analysis was conductedusing an Agilent 5110.

Results from the application of the above described method are depictedin FIG. 13 .

While specific embodiments of the invention have been described hereinfor the purpose of reference and illustration, various modificationswill be apparent to a person skilled in the art without departing fromthe scope of the invention as defined by the appended claims.

REFERENCES

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The invention claimed is:
 1. A process for the preparation of asulfur-doped carbonaceous porous material, the process comprising thesteps of: i) preparing a sulfur-based polymer by reacting elementalsulfur with one or more organic crosslinking agents, wherein the organiccrosslinking agent(s) comprises two or more carbon-carbon double bonds;ii) carbonising the sulfur-based polymer of step (i) in the presence ofat least one porosity enhancement agent selected from one or more ofpotassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide(LiOH), rubidium hydroxide (RbOH), caesium hydroxide (CsOH), magnesiumhydroxide (Mg(OH)₂), calcium hydroxide (Ca(OH)₂), potassium carbonate(K₂CO₃), sodium carbonate (Na₂CO₃), aluminium hydroxide (Al(OH)₃), zinchydroxide (Zn(OH)₂), barium hydroxide (Ba(OH)₂), phosphoric acid, sodiumchloride, calcium chloride, magnesium chloride or zinc chloride; whereinthe mass ratio of sulfur-based polymer to porosity enhancement agent instep (ii) of the process is between 3:1 and 1:3; wherein thecarbonisation of step (ii) is carried out under an inert atmosphere; andwherein the sulfur-doped carbonaceous porous material comprises greaterthan or equal to 12 wt % sulfur and comprises micropores and mesopores.2. The process according to claim 1, wherein the porosity enhancementagent is an inorganic base, an inorganic acid or an inorganic salt. 3.The process according to claim 1, wherein the carbonisation of step (ii)is conducted at a temperature of between 500° C. and 1000° C.
 4. Aprocess according to claim 1, wherein the mass ratio of sulfur-basedpolymer to porosity enhancement agent in step (ii) of the process isbetween 2:1 and 1:2.
 5. The process according to claim 1, wherein thesulfur-based polymer is carbonised for a duration of between 30 minutesand 5 hours.
 6. The process according to claim 1, wherein the mass ratioof elemental sulfur to organic crosslinking agent in step (i) of theprocess is between 20:80 and 95:5.
 7. The process according to claim 1,wherein the one or more organic crosslinking agents of step (i) of theprocess comprises two double bonds.
 8. The process according to claim 1,wherein the sulfur-based polymer of step (i) is formed by reactingelemental sulfur with one organic crosslinking agent.
 9. The processaccording to claim 1, wherein the sulfur-based polymer of step (i) isformed by reacting elemental sulfur with one or more organiccrosslinking agents at a temperature of greater than or equal to 120° C.10. The process according to claim 1, wherein the sulfur-based polymerof step (i) is a solid.